Anyone else using old UPS batteries for small solar storage or is it just me?

Been doing exactly this for a couple of years now for my shepherd's hut setup. Grabbed a load of 12V sealed lead-acid units from a local IT firm when they were upgrading their server room UPS systems — they were basically giving them away.

The honest truth is they're a bit of a lottery. Some tested at 70-80% capacity which is perfectly usable, others were basically paperweights. Worth getting a proper battery analyser before you commit to building anything around them.

A few things I've learned the hard way:

• Match your batteries carefully — mixing different ages/capacities in a bank causes headaches
• They don't like deep discharge, so keep your low-voltage cutoff generous (I run mine at 12.1V)
• A decent Victron BMV monitor is worth every penny for keeping an eye on state of charge
• They're heavy. Obvious but I ignored this and deeply regretted it when wiring up the hut

For emergency backup they're brilliant honestly — low stakes, low cost, good enough. I wouldn't try to run a whole household off them but for lighting, phone charging, a small 12V fridge? Absolutely fine.

The environmental argument is decent too — keeping these out of landfill a bit longer feels worthwhile.

Curious whether anyone else is sourcing them from similar places? I've heard data centres and hospitals are good for retired UPS stock but haven't cracked that supply chain yet. Anyone got contacts or know the best way to approach companies about end-of-life batteries?

@JA_Solar welcome to the forum — good to see someone else not afraid to get their hands dirty with salvaged kit.

Done similar myself on the narrowboat before I moved to Fogstar lithium. UPS lead-acids can be decent stopgap storage if you test capacity properly before committing them into a system — a lot come out of server rooms already half-knackered because they've been float-charged for years and never properly cycled.

Few things worth checking:

• Actual usable capacity vs rated — expect 40-60% of label on older units
• Internal resistance — high IR cells aren't worth the hassle
• Matched banks — don't mix ages or brands in the same string

What voltage system are you running on the hut? And are you monitoring state of charge properly or just winging it?

@JA_Solar this takes me right back to how I got started with my static caravan setup. Stumbled across a skip outside a data centre in Swindon with four perfectly healthy 12V sealed lead-acid units just sitting there, destined for landfill.

Ran them in a 24V bank for nearly two seasons before capacity started dropping off noticeably. The trick I found was load-testing every single one with a proper discharge cycle before committing them to the bank — the duff cells will catch you out otherwise and drag the whole lot down.

Worth mentioning, a basic battery capacity tester from Amazon saved me more headaches than I can count. Anything showing below 60% of rated capacity went straight back in the reject pile, no exceptions.

Free storage is free storage, but only if you're selective about what you're actually keeping.